Electrical coil



Aug. 25, 1970 BOND TAB TO FLANGE PLACE FLANGES I ON CORE BOND FLANGE-IS TO CORE INSERT START WIRE THROUGH POUCH WIND WIRE ONTO BOBBIN A. J, SPARLING 3,525,965

ELECTRICAL COIL Filed Aug. 16, 1968 mvnvroa ARTHUR J. SPARL l/VG ATTORNEY United States Patent 3,525,965 ELECTRICAL COIL Arthur J. Sparling, Manhattan Beach, Calif., assignor to Teledyne, Inc., Hawthorne, Calif., a corporation of Delaware Filed Aug. 16, 1968, Ser. No. 753,154 Int. Cl. H01f 27/30 US. Cl. 336-498 8 Claims ABSTRACT OF THE DISCLOSURE An electrical coil in which an insulated pouch for the start wire is formed in the bobbin by providing an insulator tab bonded over only part of its area to the inner side of one flange of the bobbin.

This invention relates to electrical coils, and more particularly to an improved manner for insulating the lead wire in coils such as are used in electrical relays.

The magnetic force for moving the armature of an electrical relay is conventionally supplied by a coil formed by winding many layers of fine wire on a bobbin. For economic reasons, and also because of size and space limitations, electrical insulation between adjacent turns and layers of wire is provided by a thin coating of insulative material, such as Teflon, which is coated directly on the wire. This coating provides suflicient insulation throughout most of the winding, since the voltage drop between adjacent turns and layers is relatively slight.

However, there is one place in the winding which requires much greater insulation strength than the other portions of the coil. This is where the end of the wire, which is conventionally called the start wire, is brought out from the center of the coil to the exterior so that an electrical connection may be made to both ends of the coil. As this start Wire comes out of the center of the coil, it touches layer after layer of wire, finally contacting the outer layer of wire on the coil. At this time, the insulation on the start wire must withstand the entire voltage drop across the coil. Further, it must withstand the voltage induced in the coil when the current through the coil is abruptly shut 01?. This induced voltage, though for only a short duration, can be larger than the normally applied voltage.

Obviously, it would be quite uneconomic to insulate the entire wire sufiiciently to withstand the potential drop to which the insulation on the start wire is subjected. This problem has long been recognized in the prior art, and many expedients have been suggested to overcome the problem.

One approach suggested by the prior art is to provide a slot or protected passage in the flange of the bobbin. In the winding process, the start wire is then brought through this slot to the core of the bobbin as an initial step in the winding operation. The flange of the core then insulates the start wire from the outer layers of the wire.

This approach is limited to coils in a size category which permits the use of molded bobbins. Smaller miniature coils use fabricated bobbins built up from an assem- 3,525,965 Patented Aug. 25, 1970 bly of spiral wrapped and bonded tubing and Washers which permit wall thickness as thin as .001 inch, as compared to perhaps .010 inch that might constitute a practical minimum for molded bobbins. Such small coils have traditionally been wound by a costly procedure whereby a small rectangular strip of insulative material is manually fastened down on top of the start wire. This is a difiicult, time consuming operation which is consequently costly, and it also fails to assure high reliability in that the operators frequently fail to get the start wire securely under the insulative strip.

It is accordingly an object of the present invention to provide an improved electrical coil.

It is another object of the present invention to provide an improved means for insulating the start wire of an electrical coil.

It is yet another object of the present invention to providle an improved method for manufacturing electrical cm s.

It is still another object of the present invention to effect the above mentioned objects while decreasing the cost of manufacturing electrical coils.

Briefly stated, and in accordance with one embodiment of the present invention, an electrical coil is manufactured in which the bobbin is formed from two washer-like flanges and a cylindrical core. An insulator tab is provided and is attached over only a portion of its surface to the inner surface of one of the flanges of the bobbin. Preferably, the insulator tab is attached to the flange before the flange is attached to the core to form the bobbin. An insulated pouch is thus formed between the flange and that area of the tab which is not attached to the flange. The start wire is then fed through this pouch to the core of the bobbin at the beginning of the winding operation.

For a complete understanding of the invention, together with other objects and advantages of the invention, attention is directed to the attached drawings, in which:

FIG. 1 is a perspective view of a bobbin of an electrical coil incorporating the presently preferred embodiment of the present invention onto which several turns of magnet wire have been wound;

FIG. 2 is a plan view of the insulator tab shown in FIG. 1 and shows how the tab is bonded to the flange of the bobbin to form an insulated pouch;

FIG. 3 is a sectional view of a bobbin similar to that shown in FIG. 1 but which incorporates a second embodiment of the invention; and

FIG. 4 shows, in block diagrams, the method of manufacturing electrical coils in accordance with the present invention.

Now describing FIG. 1, therein is shown a perspective View of a bobbin for an electrical coil, such as might be used in a miniature relay, onto which a few turns of magnet wire have already been wound. The shown bobbin incorporates the presently preferred embodiment of the invention.

The bobbin 10 is formed from a central core 12 and flanges 14 and 15. Core 12 is cylindrical and flanges 14 and 15 are washer-shaped. In accordance with the present invention, there is attached to the inner side of flange 14 an insulator tab 16. As will be later described in more detail, insulator tab 16 is bonded to flange 14 over only a portion of their contiguous areas such that an insulated pouch is formed between the adjacent unbonded surfaces of tab 16 and flange 14.

FIG. 1 also shows several turns of the wire 18 which forms the electrical coil wound onto bobbin 10. The wire 18 is conventionally termed the magnet wire of the coil. The start end 20 of magnet wire 18 is shown brought through the insulated pouch and terminating a suitable length from bobbin 10. A heavier lead wire may later be attached to start wire, if desired. This may be done in any of the manners known in the prior art. Since it forms no part of the present invention, no such manner will be described.

FIG. 2 shows a plan view of the insulator tab 16 and also shows how the insulated pouch is formed by bonding the tab 16 over only a portion of its area contacting the flange of the bobbin. As shown therein, tab 16, in its presently preferred embodiment, basically comprises two parts, a sector 22 of a washer and a rectangular portion 24. Tab 16 is bonded to flange 14 over the shaded area 26. It has been found that the insulated pouch is best formed and the manufacturing operation best effected by making the sector approximately 300. The rectangular portion 24, as is shown in FIG. 1, extends well beyond the outer edge of flange 14 when tab 16 is bonded to the flange. After the winding operation is complete, portion 24 is bent over the wound coil to form an insulating patch over the coil.

As shown in FIGS. 1 and 2, the unbonded portion of tab 16 includes a nose portion 25 which extends in the opposite direction from rectangular portion 24 than does the bonded area 26. The provision of nose 25 greatly facilitates the manufacturing operation. It permits the start end 20 of magnet wire 18 to be placed in the insulated pouch in a quick, sure and simple manner and insures that the wire does not get hung up on the edge of tab 16 where it might contact outer layers of the wire 18. It is especially important in miniature coils that the start end 20 can be quickly and surely placed in the pouch, since magnet wire 18 might be so small as to require optical magnification to be seen. Thus, the provision of nose portion 25 eliminates the need for a time consuming, and thus expensive, inspection at this point in the assembly operation.

As is better shown in FIG. 1, in the presently preferred embodiment, the outer diameter of sector 22 is substantially equal to the outer diameter of flange 14. This provides an integral bobbin structure which is easy to handle in the manufacturing operation. Preferably, core 12, flanges 14 and 15 and tab 16 are all made from a two layered material in which one layer is a relatively stiff material which has a relatively high melting temperature. This layer serves as a base for the bobbin. The second layer is a thermally bondable material which bonds at a substantially lower temperature. In this manner, the bobbin 10 can be manufactured from simply shaped components each of which can be economically made. As is later described in more detail, these components are then assembled and bonded together with heated dies and tools. These heated dies and tools melt the thermoplastic layer of the components and they are bonded into a unitary structure which is, in effect, a molded one place bobbin, but which is much cheaper to manufacture than a true molded bobbin.

In the preferred embodiment, the base layer is a polyimide film sold by Du Pont under the trade name Kapton. This material goes to zero strength at about 1500 F. and vaporizes at a somewhat higher temperature. The thermoplastic layer is preferably a fluorocarbon resin made by combining tetrafluoroethylene and hexafluoropropylene which is sold by Du Pont under the trade name FEP, and which melts at about 500 F.

FIG. 3 shows a sectional view of a bobbin 10 similar to that shown in FIG. 1 but which incorporates a second embodiment of the present invention. As shown therein, the insulator tab 28 is trapezoid shaped with its angled side positioned along the surface of core 12. Tab 28 is bonded to flange 14 at the shaded area 30. The insulated pouch is formed between the unbonded areas. The start end of the magnet wire (not shown in this figure) is again positioned in the pouch so formed.

FIG. 4 shows, in block diagram, the process by which an electrical coil is manufactured in accordance with the present invention. As shown therein, the insulator tab is first bonded to the flange to form the insulated pouch. Preferably, this is done with a heated die having a surface coextensive with the shaded areas of FIGS. 2 and 3 which represent the areas to be bonded together. This flange and the other flange are then placed upon the ends of the core and are attached to the core. Preferably this is done by first flaring the ends of the core with a rotating, conical-shaped tool, in a conventional manner, and then bonding the flanges to the flared ends of the core with a heated tool.

Next, the start end of the magnet wire is fed through the insulated pouch and the magnet wire is then wound onto the bobbin. Numerous methods are known in the art for actually winding the wire onto the bobbin, and any suitable one of these known methods may be used with the present invention. Since the actual winding per se of the wire forms no part of the present invention, no particular method is shown herein.

After the coil is wound, lead wires may be attached to it and it may be attached to a relay frame as desired. Again, since these operations form no part of the present invention, they are not shown herein.

The present invention has thus been disclosed and two embodiments described in detail. However, it is not intended that the invention be limited to these shown embodiments. Instead, many modifications will be apparent to those skilled in the art. Accordingly, it is intended that the invention be limited in spirit and scope only by the appended claims.

What is claimed is:

1. In an electrical coil which includes a magnet wire wound about a bobbin, said magnet wire including a start Wire, and the bobbin includes a central core having a flange at each end thereof, the improvement comprising means for insulating said start wire from other adjacent portions of said magnet wire, comprising an insulator tab attached to the inner surface of one of said flanges, said tab being attached to said inner surface over only a portion of its area contacting said flange, thereby forming an insulated pouch between the adjacent unattached areas of said tab and said inner surface, said start wire being positioned in said insulated pouch.

2. The invention of claim 1 in which said flange is washer shaped and said insulator tab includes a portion which is a sector of a washer.

3. The invention of claim 1 in which the unattached portion of said insulator tab includes a nose shaped portion extending arcuately away from the attached portion of said insulator tab.

4. The invention of claim 2 in which said sector is approximately a 300 sector.

5. The invention of claim 2 in which said insulator tab further comprises a second portion extending beyond the outer diameter of said flange.

6. The invention of claim 1 in which said bobbin is constructed from a material comprising a first layer of a relatively stiff dielectric material capable of withstanding a relatively high temperature coated with a second layer of a thermally bonding dielectric material having a relatively low bonding temperature.

7. The method of manufacturing an electrical coil which comprises the steps of bonding an insulator tab to a flange over only a portion of the areas of said tab adjacent to said flange, whereby an insulated pouch is formed between the adjacent unbonded areas of said tab and flange, attach- 5 6 ing said flange to a core to form a bobbin, inserting the 3,179,634 4/1965 Edwards. start end of a magnet wire through said pouch, and wind- 3,208,036 9/1965 Harrison 336-192 X ing said magnet wire onto said bobbin. 3,407,372 10/1968 Elvers 336-492 X 8. The invention of claim 1 in which said insulator tab 3,422,215 1/1969 Humes 174-420 is substantially trapezoidal shaped and in which one end 5 OTHER REFERENCES of said tab is positioned adjacent said core and the opposed end of said tab extends beyond the outer edge of Du Pont Kapton Polyimide Film Brouchure of Du Pont C0. Release date June 1967.

said flange.

References Clted ELLIOTT GOLDBERG, Primary Examiner UNITED STATES PATENTS 10 1,130,268 3/1915 Haefely -3 339--198 X 2,667,624 1/1954 Bezs 336192X 29605;242-118.8;336208 

